1. Field of the Art
This invention relates to an ultrasound internal examination system having an ultrasound probe to be endoscopically inserted into an intracavitary portion of human body or the like for ultrasound examination.
2. Prior Art
Generally, ultrasound internal examination systems are largely constituted by an ultrasound probe with an ultrasound transducer element for transmission and reception of ultrasound signals, a signal processor which has the function of controlling the transmission and reception of the ultrasound signals in addition to the function of processing received echo signals, and a monitor for displaying ultrasound images. There has been known in the art the so-called insert type ultrasound probe which is designed to be introduced into an intracavitary portion of interest, directly or through a guide means such as an endoscope or the like, and to transmit ultrasound pulses into tissues of an intracavitary portion or wall while receiving reflected echo signals. In this connection, the scan modes of ultrasound examination systems includes the so-called B mode scan in which ultrasound pulses are transmitted into an intracavitary wall portion at predetermined time intervals from an ultrasound transducer which is being moved over a predetermined scan range, and, on the basis of return echoes, an ultrasound image of the scan range is displayed on a monitor screen. For this scan mode of the ultrasound transducer, either a mechanical scan system or an electronic scan system is usually employed.
An insert type ultrasound probe of an extremely small diameter, which is intended to be inserted through a biopsy channel of an endoscope like forceps, is known, for example, from U.S. Pat. No. 4,802,487. In the ultrasound probe of this sort, there have been strong demands for further reductions in diameter and length of rigid portions on the probe, and therefore there has been no choice but to employ a single-element ultrasound transducer of small size, instead of an arrangement involving a large number of transducers as in the electronic scan system. It follows that the ultrasound probe of this type is necessarily arranged to operate with a mechanical scan system. With regard to its scanning direction, it can be put in a radial scan in which the ultrasound transducer is turned about an axis or in a linear scan in which the ultrasound transducer is moved linearly. In case of the radial scan, the scan range may extend to 360.degree. or may be restricted to an arc of a predetermined angle.
The ultrasound examination system is usually resorted to in checking for the existence of a tumor or other diseased portion which normally has a certain degree of three-dimensional spreading, so that it is important to grasp the condition of an affected portion three-dimensionally before giving any diagnosis. However, a single-element ultrasound transducer can give only one tomographic ultrasound image in one direction of an intracavitary portion no matter whether it is in radial scan or in linear scan. To overcome this problem, attempts have been made to get a three-dimensional image of a diseased portion from a plural number of tomographic images which are taken through an ultrasound transducer at a number of different positions. For example, in a radial scanning operation, ultrasound tomographic images are sequentially taken while moving an ultrasound transducer gradually in the linear direction. However, it has been found extremely difficult to take ultrasound tomographic images accurately at uniformly spaced positions even with meticulous skills, failing to recognize the shape or other conditions of a diseased portion by way of a three-dimensional image which correctly reflects the actual condition of the disease if any.